WASHINGTON  The federal Superfund program for the nation's worst hazardous waste sites spent $507 million and finished cleaning up 40 of them last year.

That leaves 1,237 sites still to go, the Environmental Protection Agency said in a report Tuesday to Congress. Since the program began in 1980, more than 900 toxic messes have been cleaned up.

Superfund cleanup completions have declined to 40 during each of the past two years, compared with 42 completions in 2002 and 47 in 2001. During the preceding Clinton administration, EPA completed an average 76 cleanups a year.

EPA officials have repeatedly cited the increasing size and complexity of the decontamination sites as reasons for completing fewer cleanups.

For all the nation's hazardous waste sites, not just those in the Superfund program, EPA reported in December that it would probably take up to 35 years and $280 billion to fix most of the nation's existing and yet-to-be-discovered hazardous waste sites.

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It estimated that there were 77,000 such sites, with up to 9,267 more discovered each year.

Less than 1 percent of the projected average number of sites that would need to be decontaminated over the next three decades are part of the Superfund program. About 43 percent of those sites are underground storage tanks that are leaking or might leak.

By spending, however, the Superfund sites would account for about 15 percent of the projected average, EPA has said.